1. Technical Field
The present invention relates to a wireless communication, and more particularly, to transmission opportunity (TXOP) in a mesh network.
2. Discussion of Related Art
With the advancement of information communication technologies, various wireless communication technologies have been developed. Among the wireless communication technologies, there is a wireless local area network (WLAN) that is a technology whereby super high-speed Internet access is possible in a wireless fashion in homes or businesses or in a region providing a specific service by using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc.
A mesh network can be defined as a network which supports direct communication between a plurality of wireless devices having a relay function not via an access point (AP). Functionally, a distribution system (DS) of the AP can be replaced with an interoperable wireless link or a multi-hop path between the plurality of wireless devices. According to the mesh network, any one of the wireless devices can establish an interoperable peer-to-peer wireless link with other neighboring wireless devices and/or APs. Therefore, there is an advantage in that a wireless connection can be more flexibly established.
In the mesh network, one wireless device can be connected to other wireless devices and thus can have a plurality of communication paths. Such a communication path between the wireless devices is also referred to as a wireless mesh link, or simply a mesh link or a peer link. Although such a wireless device is referred to as a mesh point (MP), the term is not limited to the MP. If the MP provides a function of an access point (AP) in addition to the aforementioned relay function, the MP is referred to as a mesh access point (MAP).
Such a mesh network has many advantages, e.g., flexibility of network implementation, reliability caused by a detour path, and reduction of power consumption resulted from a decreased communication distance, etc. More specifically, by using the mesh network, a network can be flexibly implemented between MPs in a place where there is no existing communication network. In addition, the mesh network can ensure a plurality of detour paths due to interconnections among a plurality of MPs. Therefore, even if one MP is erroneous, data can be transmitted through another path. Further, since the mesh network can perform communication via a neighbor MP even if a coverage of one MP is not large enough, telecommunication can be achieved with low power.
IEEE (Institute of Electrical and Electronics Engineers) 802.11 standard is well known in the WLAN. The architecture of the MAC sublayer in the IEEE 802.11 includes the distributed coordination function (DCF), the point coordination function (PCF), the hybrid coordination function (HCF), and their coexistence. The HCF uses both a contention-based channel access method, called the enhanced distributed channel access (EDCA) mechanism for contention-based transfer and a controlled channel access, referred to as the HCF controlled channel access (HCCA) mechanism, for contention-free transfer. EDCA may contends for transmission opportunities (TXOPs). This means that a plurality of MPs may use same TXOPs. A TXOP is an interval of time when a particular quality of service (QoS) station has the right to initiate frame exchange sequences onto the wireless medium (WM). The TXOP is either obtained by the station by successfully contending for the channel or assigned by the hybrid coordinator (HC). Contention (or collision) may cause delay of services and degradation of QoS.
In a mesh network, contentions may occur in multiple hop range. There is a need to mitigate collision in a contention-based mesh network.